1. Field of the Invention
The present invention relates generally to a cathode ray tube and more particularly to a cathode ray tube with an electron beam reflection film in the form of a bismuth oxide thin film having a high bulk density on the electron beam collision side of a color selective electrode assembly and a method of producing the same.
2. Description of the Prior Art
When three electron beams emitted from an electron gun in a typical cathode ray tube are projected on a phosphor layer formed on the inner face of a panel portion through electron beam passing openings of a color selective electrode assembly such as a shadow mask, a pixel portion of the phosphor layer onto which the electron beams are projected becomes luminous, so that the phosphor layer as a whole displays a desired colored image.
In such an image display, the transmittance of the electron beams through the aforementioned shadow mask is of the order of from 10 to 20%. However, the electron beams which have failed to pass through the electron beam apertures of the color selective electrode assembly and collided with the color selective electrode assembly flow in the color selective electrode assembly in the form of an electric current, thus causing the color selective electrode assembly to undergo thermal expansion because of the Joule s heat resulting from the current. As a result, the positional relationship between the color selective electrode assembly and the phosphor layer formed on the inner face of the panel portion slightly varies and the electron beams projected onto the phosphor layer commit landing errors. The landing errors of the electron beams cause a shift in color in the display image and this phenomenon is called mask doming. Due to the mask doming thus caused in the display image on the cathode ray tube, not only the purity of color of the display image but also the white uniformity thereof may greatly deteriorate.
A known mask-doming suppressing means used in such a cathode ray tube is adapted to reducing the electron beam energy given to the color selective electrode assembly, that is, suppressing the thermal expansion of the color selective electrode assembly by employing a metal having a low thermal expansion coefficient such as invar for the color selective electrode assembly and coating the electron beam collision side of the color selective electrode assembly with an electron beam reflection film, whereby the quantity of mask doming is lowered.
There are a first, a second, a third and a fourth method of forming the aforementioned electron beam reflection film as disclosed in Japanese Patent Laid-Open Nos. 80438/1988, 80439/1988, 75132/1990 and 283526/1987, respectively.
According to the first method above, bismuth oxide (Bi.sub.2 O.sub.3) put on an evaporation cell of stainless steel is subjected to radio-frequency heating, and deposited by vacuum deposition on a shadow mask.
According to the second method above, bismuth oxide (Bi.sub.2 O.sub.3) on a tungsten boat is subjected to resistor heating, and deposited by vacuum deposition on a shadow mask.
According to the third method above, a sintered pellet of bismuth (Bi) powder on a tungsten boat is subjected to resistor heating and bismuth (Bi) is deposited by vacuum deposition on one side of a shadow mask as an electron beam reflection film.
According to the fourth method above, suspension of bismuth oxide (Bi.sub.2 O.sub.3) powder together with slurry containing water glass acting as a binder is sprayed by means of a spray-gim so as to form a coating layer of bismuth oxide (Bi.sub.2 O.sub.3) on one side of a shadow mask as an electron beam reflection film.